The invention relates to a method for operating an internal combustion engine and especially of a motor vehicle wherein the fuel is infected into a combustion chamber in at least two operating modes and wherein there can be a switching between the two operating modes. Likewise, the invention relates to an internal combustion engine especially for a motor vehicle wherein fuel can be injected into a combustion chamber in at least two operating modes. The engine has a control apparatus with which a switchover between the modes of operation can be effected.
A method of this kind and an engine of this kind are known, for example, from a so-called gasoline direct injection. There, fuel is injected into the combustion chamber of the engine in a homogeneous operation during the induction phase or in a stratified operation during the compression phase. The homogeneous operation is preferably provided for the full-load operation of the engine; whereas, the stratified operation is suitable for the idle operation or part-load operation. In such a direct injecting engine, a switchover is made between the above-mentioned modes of operation, for example, in dependence upon the requested torque.
The different modes of operation of the engine place different requirements on the control (open-loop and/or closed-loop) of a throttle flap arranged in the intake manifold. Accordingly, it is, for example, advantageous that the throttle flap is opened as wide as possible in stratified operation in order to reduce the fuel consumption as much as possible. However, it must be avoided that specific functions of the engine no longer function because of a throttle flap which is open too wide because of the occurring pressure conditions. Such specific functions are, for example, an exhaust-gas recirculation or a tank venting.
In homogeneous operation, a constant air/fuel ratio is run, that is, xcex=1. There, a fixed ratio is present between the fuel quantity and the air quantity which is controlled (open-loop and/or closed-loop) via the throttle flap. In the stratified operation, lambda should have a lowest value above 1 because of exhaust-gas reasons. From this, a minimum opening of the throttle flap results. On the other hand, a certain throttling should make possible the above-mentioned other functions. From this, a maximum lambda value results.
It is an object of the invention to provide a method for operating an internal combustion engine with which the least possible consumption of fuel is attainable with a low development of toxic substances without other functions of the engine being hereby disadvantageously affected.
The method of the invention is for operating an internal combustion engine including an engine for a motor vehicle. The method includes the steps of: injecting fuel into the combustion chamber in at least two operating modes and switching between the operating modes; determining a desired value (rlmd$s) for the air charge in the combustion chamber with the desired value (rlmd$s) defining a maximum value for the air charge in the combustion chamber which may not be exceeded.
In an advantageous embodiment of the invention, a desired value is determined for the maximum permissible air charge of the combustion chamber in dependence upon functions of the engine, for example, in dependence upon an exhaust-gas recirculation and/or a tank venting and/or the like. This desired value defines that desired value for the air charge which is maximally permissible based on the functions of the engine. In this way, it is ensured that none of the functions of the engine becomes inoperable because of a throttle flap which is opened too wide.
In an advantageous further embodiment of the invention, a minimum value selection is carried out on which the desired value for the air charge in the combustion chamber, which is required for the generation of the torque requested from the engine, and the desired value for the maximum permissible air charge of the combustion chamber participate. In this way, the lesser of the two desired values is selected. In this way, it is ensured that lambda in homogeneous operation does not become greater than one.
In an advantageous embodiment of the invention, a desired value for the air charge in the combustion chamber is determined. The desired value defines a minimum value for the air charge in the combustion chamber beneath which the air charge does not drop.
The desired value is preferably that desired value for the air charge which is at least required for generating a combustion in the combustion chamber. In this way, it is ensured that the air charge in the combustion chamber is, in each case, so great that a combustion of the fuel, which is injected into the combustion chamber, reliably takes place. Defective ignitions or the like are thereby avoided.
In a further advantageous embodiment of the invention, a maximum value selection is carried out in which the desired value for the air charge participates. This desired value is the least required for generating a combustion in the combustion chamber. In this way, it is ensured that, in no event, will there be a drop below the air charge in the combustion chamber which is required for generating a combustion.
In further advantageous embodiments of the invention, the desired value for the air charge is determined in dependence upon the mode of operation of the engine and/or an opening of the throttle flap is requested by each of the functions of the engine. The desired value is determined in dependence upon the smallest opening.
It is especially advantageous when a minimum value selection is executed on which the throttling, which is requested by the functions, participates. In this way, that throttling is determined which may be maximally present so that all participating functions of the engine function reliably.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an internal combustion engine, especially of a motor vehicle. A program is stored on the control element which can be run on a computing apparatus such as a microprocessor and is suitable for carrying out the method of the invention. In this case, the invention is therefore realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same manner as the method for the execution of which the program is suitable. As a control element, especially an electrical storage medium can be applied such as a read-only-memory.
Additional features, possibilities of application and advantages of the invention result from the description of the embodiments of the invention which follows. The embodiments are shown in the figures of the drawing. All described or illustrated features define the invention by themselves or in any desired combination independently of their composition in the patent claims or their dependency as well as independently of their formulation or description in the disclosure and/or drawings.